This invention relates to a hopper discharge apparatus or outlet for the bottom of hopper cars, and more particularly, to a retrofit kit for a pneumatic outlet with the kit employing an air permeable fluidizing membrane on opposite sides of the outlet with an externally mounted common manifold assembly supplying fluidizing air to the membranes.
It is well known that over the road hopper trucks and covered hopper railway cars are provided with pneumatic or gravity discharge systems to unload various types of transported product. Where ladings including powdered or pulverant products, such as flour or the like, are unloaded, it is often advantageous that the unloading systems should fluidize the lading in order to facilitate the removal and discharge of the lading from the hopper car. This generally means that low pressure air must be introduced through air permeable membranes located in the discharge apparatus to fluidize the lading (i.e., to cause the powdered lading to flow like a liquid) thereby to permit quick and efficient unloading of ladings that tend to bridge or column during discharge. In bridging (arching) or columning (rat holing), particles of the lading interlock and resist flow because of their own weight. Some kind of assistance is needed to reduce these bridging and columning forces, and this is where fluidization, employing air permeable fluidizing members become an important part of the unloading system.
Examples of prior art designs which employ air permeable fluidizing membranes in hopper cars to facilitate unloading are shown in U.S. Patent Nos. 4,015,751, 4,280,706 and 4,568,224. Each of these patents shows an air permeable fluidizing membrane which is positioned on sloping surfaces of the pneumatic discharge outlet to allow low pressure air to be introduced into powdered lading that tend to clog the unloading outlet. While these constructions have worked quite well for their intended purpose, they have required specialized discharge outlet constructions which are not only costly to build, but expensive to maintain. There are a large number of non-fluidized pneumatic discharge outlets now being used on railroad cars, for example; however, they have not been used where fluidized lading systems are required, nor have they been capable of being converted to fluidized unloading systems.
In addition to the aforementioned prior art problems, it is also well known that the air permeable fluidizing membranes have been either fabric pads or stainless steel mesh membranes. The stainless steel fluidizing membranes are easily cleaned with soap, water or stronger chemicals without harm, and because the membrane is steel, not fabric, it will not retain undesirable moisture. Also with stainless steel, there is no danger of lint or fiber contamination. Yet, stainless steel membranes are costly, not only during the initial manufacture, but also in replacement, which is not infrequent. Sometimes, in cleaning hopper cars, workmen step on the air permeable fluidizing membranes, immediately requiring a replacement. An air permeable fluidizing membrane which could perform in the same way as the stainless steel fluidizing membranes, at a much lower cost, would be desirable.